New, more stringent emission limits for diesel engines necessitate the use of exhaust after-treatment devices. One such after-treatment device is a diesel particulate filter (DPF), which removes fine carbon particles (soot) and other diesel particulate matter from the exhaust gases emitted from a diesel engine. As exhaust gases pass through a DPF, particulate matter is removed from the exhaust gases and deposited onto the interior walls of the filter.
Many after-treatment devices undergo periodic regeneration cycles, during which accumulated particulate matter is removed from the device. A regeneration cycle can be passive, active, or a combination thereof. Passive regeneration removes particulate matter through the use of a catalyst. Active regeneration uses a fuel burner to heat the exhaust gases passing through the filter to a temperature that causes the particulate mater to combust.
During an active regeneration cycle, the temperature of the exhaust gas plume may rise significantly above acceptable temperatures normally experienced by exhaust systems without such after-treatment devices. As an example, exhaust systems without after-treatment devices typically discharge exhaust gas at a temperature of around 650 degrees Kelvin. In contrast, an exhaust system having an after-treatment device that includes an active regeneration cycle may experience an exhaust gas plume temperature exceeding 900 degrees Kelvin at its center core. The elevated exhaust gas temperature also increases the surface temperature of the exhaust system components.
It is desirable to decrease the temperature of the exhaust gas plume, and thus, the temperature of the surface of the exhaust system components. Presently known exhaust cooling systems generally lower exhaust gas temperatures by mixing ambient air with the exhaust gases near or after discharge from the exhaust system, and are therefore ineffective in reducing the temperature of the surfaces of the exhaust components. Thus, there exists a need for an exhaust cooling system that lowers the temperature of both the discharged exhaust gases and also the exhaust component surfaces.